The present invention relates to a fiber Bragg grating system, particularly to a high-resolution fiber Bragg grating sensor system with a linear-cavity fiber laser scheme. Therefore, this invention can be employed to monitor temperature variation (such as controlling for medical engineering, civil engineering, industrial sensor, and monitoring the process of silicon wafer), strain variation (such as measuring for stratum slide and structural stress), and fiber communication network (such as monitoring for the reliability of the transmission data on network).
Lately, the fiber Bragg grating has become an important optical device in the field of fiber sensor. Its characteristic is that, when under temperature varying or strain varying, the Bragg wavelength will be varied so as to apply the optical device produced by such fiber sensor in a wider field, such as in the field of variation of strain and temperature etc. The traditional fiber Bragg grating sensor system adapts broadband light source for measuring its optical power reflectivity. In general, it uses a tunable Fabry-Peror filter to be a detection device, which may transfer the reflectivity from a frequency domain to a time domain. It can be read by the present electric technology. However, according to such system, it may be limited to develop by the Fabry-Peror filter and/or the electric technology (such as the design of circuit).
John W. Berthold et al., U.S. Pat. No.: 5,845,033, Fiber optical sensing system for monitoring restrictions in hydrocarbon production systems, which discloses a system being adapted for monitoring hydrocarbon in accordance with a fiber Bragg grating system. Thus, it can obtain a fact of commercial value of the fiber sensor, which is more useful.
Alan D. Kersey et al., U.S. Pat. No.: 5,748,312, Sensing apparatus and method for detecting strain between fiber Bragg grating sensor inscribed into an optical fiber, which discloses sensing apparatus for monitoring physical quantities of multipoint by a plurality of fiber Bragg grating serially connected, such as pressure and temperature etc. Thus, it can obtain another fact of commercial value of fiber sensor for sensing in a greater area.
Michael A. Sapack et al., U.S. Pat. No.: 6,072,567, Vertical seismic profiling system having vertical seismic profiling optical signal processing equipment and fiber Bragg grating optical sensors, which discloses a seismic profiling system designed in accordance with fiber Bragg gratings. For those countries located in the seismic area, it can be very useful for seismic prediction.
M. A. Putnam et at., in xe2x80x9cOptical Fiber Conference 1997 (OFC 97xe2x80x2)xe2x80x9d, has provided an article of xe2x80x9cSensor grating array demodulation using a passively mode-locked fiber sensorxe2x80x9d, which discloses a circle structure of fiber laser formed by a plurality of fiber Bragg grating serially being connected. However, in this article, the structure is complex, and it costs high.
T. Kurashima et al., in xe2x80x9cIntegrated Optics and Optical Fiber Communicationsxe2x80x9d, has provided an article of xe2x80x9cDistributed strain measurement using BOTDR improved by taking account of temperature dependence of Brillouin scattering powerxe2x80x9d, which discloses a Brillouin scattering technology for distributed fiber sensor for strain and temperature. However, this kind of technology costs very high, and is limited to be suitable for civil infrastructure in long distance, such as high speed rail, bridges, and tunnels etc.
G. A. Johnson et al., in xe2x80x9cIEEE Journal of Lightwave Technologyxe2x80x9d, vol. 18, No. 8, pp. 1101xcx9c1105 (2000), has provided an article of xe2x80x9cFiber Bragg Grating Interrogation and Multiplexing with a 3xc3x973 Coupler and a Scanning Filterxe2x80x9d. It employs reflecting spectra of fiber Bragg grating to analyze the variation of temperature and pressure. It uses a tunable Fabry-Peror filter to be a detection device, which is very expensive (about NT$200,000). Thus, it may cost a lot for setting such structure, and it may be limited its application.
Y. Yu et al., in xe2x80x9cIEEE Photonics Technology Lettersxe2x80x9d, vol. 13, No. 7, pp. 702xcx9c704 (2001), has provided an article of xe2x80x9cFiber-Laser-Based Wavelength-Division Multiplexed Fiber Bragg Grating Sensor Systemxe2x80x9d. It uses a detection device of tunable Fabry-Peror filter to be a light source, and it monitors temperature varying by using Michelson interferometer. By contrast, optic interfere technology is more difficult than fiber sensor system; therefore, cost and technology ability are the consideration for application.
Therefore, the present invention provides a high-resolution fiber Bragg grating sensor system with a linear-cavity fiber laser scheme.
The main object of the present invention is to provide a high sensitive sensor system.
Another object of this invention is to provide a relative cheap distributed sensor system.
The other object of this invention is to provide a multipoint independent (without interfering by electromagnetism) sensor system.
The present invention provides a fiber Bragg grating sensor system, which comprises a pump laser adapted for generating light, a first coupler connecting with said pump laser, a sensor unit including a first fiber Bragg grating connected with said first coupler, a erbium-doped fiber connecting with said fist fiber Bragg grating through said first coupler, a fiber loop mirror formed by a polarization controller and a second coupler being connected to each other, a third coupler connecting with said second coupler, a forth coupler, and a fifth coupler, a second fiber Bragg grating connecting with said forth coupler, a third fiber Bragg grating connecting with said fifth coupler, a first photodetector connecting with said second fiber Bragg grating through said forth coupler, a second photodetector connecting with said third fiber Bragg grating through said fifth coupler, and a microprocessor connecting with said first photodetector and said second photodetector.